This invention relates to an athletic shoe having a shock-absorbing running sole that has at least one component incorporated into the body of the sole so as to modify its mechanical properties of stiffness, shock absorbency and the like, as well as to a process for manufacturing said athletic shoe.
An athletic shoe having a sole representing one form of the above-explained type running sole is known from U.S. Pat. No. 4,297,796. In the case of this athletic shoe, a netting or open mesh structure made of stretch-resistant threads or similar means is connected to the top side of a flexibly deformable sole layer. The netting or mesh structure is also folded down around the periphery of the sole layer. The netting structure has the purpose of distributing the shock stresses which, in individual sections, such as in the section of the heel or in the section of the ball, are especially high, over a larger area. An athletic shoe of this type, after the manufacture, cannot be changed as far as its shock-absorbing characteristics are concerned, and, while the netting structure may serve a shock distributing function, it does not provide a means for varying the shock absorbency of localized portions of the sole.
It is also known, such as from U.S. Pat. Nos. 2,885,797; 4,364,188 and 4,364,189, as well as German Offenlegungsschrift (Laid-Open patent application) No. 29 04 540, to be able to vary the shock absorbency of localized portions of a resilient sole or sole layer (such as the midsole of a running shoe) by the subsequent incorporation of plugs of a harder material into openings formed in the otherwise homogeneous material of the body of the resilient sole. While such a technique provides a high degree of flexibility in adapting the stiffness and shock absorbency of various parts of a given sole to the needs of a given runner, it is not well suited to mass production of large numbers of soles, nor is there any load distributing effect when individual plugs are utilized. Furthermore, if a mere friction fit is used to hold the plugs in place, they may become dislodged during use, particularly in areas of the sole that are highly flexed. On the other hand, if adhesives are used, a permanent bond results that precludes re-adapting the sole to subsequent needs, not to mention the fact that the fastening procedure can be messy and time-consuming. On the other hand, if the insert plugs were to be incorporated or molded-in during formation of the body of the resilient sole, the costs and/or complexity of the molds required for every single size and/or combination of characteristics of the shoe would be dramatically increased.
This invention has an objective of adapting the stiffness and shock absorbency of a resilient sole or sole layer, particularly individual sections of the sole to the shock stress respectively experienced thereby. Furthermore, the invention seeks to attain this objective both from the mass manufacture standpoint as well as from that of enabling the shock-absorbing characteristics to be subsequently adapted to the individual physical needs of the user or to the specific type of sport for which the shoe incorporating the sole is to be used.
According to preferred embodiments of the invention, these objectives are achieved by a process and athletic shoe wherein an openwork structure, such as a meshwork or netting, is embedded into at least a portion or portions of a resilient sole during molding thereof, and plugs of a harder material than the body of the sole are inserted vertically into openings of the openwork structure, prior to and/or subsequent to molding of the sole about the openwork structure.
In spite of the use of a uniform material for the midsole, the invention makes it possible to give the different sections of the running sole different shock-absorbing characteristics according to anticipated stressing thereof. When using exchangeable plugs, it is possible that the user may find and adjust the blend of shock-absorbing characteristics that is optimal for him or her, and may still be able, according to the different running conditions, as in the case of a hard or soft ground or similar conditions, to adapt the shock-absorbing characteristics in the different sections of the sole.
Moreover, by appropriate shaping of the insert plugs, an interlocking engagement with the openwork structure can be achieved that will effectively hold subsequently inserted plugs in place within the sole without the use of adhesives; while, in the situation where the plugs are to be embedded during manufacture of the sole, they can be pre-assembled into the openwork to form pre-assmebled units in any number of combinations, thereby enabling a standardized mold to form soles possessing numerous different characteristics.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.